First Observation of $\hat{I}›$ Hyperon Transverse Polarization in $\ddot{I}ˆ(3686)\to \hat{I}›\bar{\hat{I}}›$

Abstract

Based on $(448.1\pm 2.9)\times 10^6$ $\ddot{I}ˆ(3686)$ events collected with the BESIII detector at the BEPCII collider, we present the first observation of spin transverse polarization of $\hat{I}›$ and $\bar{\hat{I}}›$ hyperons produced coherently in the decay $\ddot{I}ˆ(3686)\to \hat{I}›(\to p\ddot{I}{€}^{-})\bar{\hat{I}}›(\to \bar{p}\ddot{I}{€}^{+})$. The relative phase between the electric and magnetic hadronic form factors is measured to be $\hat{I}”\hat{I}¦=(21.0\pm 3.7_{stat.}\pm 0.8_{syst.}{)}^{\circ }$. The angular distribution parameter $\hat{I}{\pm }_{\ddot{I}}ˆ=0.83\pm 0.02_{stat.}\pm 0.01_{syst.}$ is determined with a precision improved by a factor of 3.7 compared to the previous measurement. The relative phase between the $S$- and $D$-wave amplitudes for $\hat{I}›\bar{\hat{I}}›$ is observed, and the effective interaction radius is determined to be $0.0450\pm 0.0026_{stat.}\pm 0.0012_{syst.}$ fm. These results provide new insights into the strong interaction mechanisms and the internal structure of baryons.